Solid capacitors



Aug. 13, 1963 E. J. SHERMAN 3,100,329

SOLID CAPACITORS Filed March 24. 1960 Fae-cr Pya/.Yr/c (Mmes/0N ar 14A/@Maas Mme-4r; wr/mf Pfaff ,00,655 ra MAA/64Min,' ax/pf 5r affirm/6 Pfaff 450m' 1 ,sm/arf 4r im "c,

IN VE N TOR. bw/1f@ J .Saw/14AM A Inione j .frjateaied Aue-13 ieee f f i g-layerqfSince the pellet is,recycledsevenaltimes between",` f hlsfinvention'reiaies ,to an"`inipmved method ef fab: -the electrolyte and the impregnatins Solutimindis rather ating@ solidelectrolytic*capacitorv ,1 'More particularly, .porousinnalturd it is very diioult 'topreventthe pellet rela'testo n. im pioved methodoffforming dielectric 10 from retaining some of the electrolyte, withir`1 itspores, msg n anzable' d ectrod3- .f f I n ordertoyavoid degr`adat io r 1 of the-finished' capacitors, Solid electrolyticlcapacitors have -been ,"rnade:` by elec` A r tr`oly ti 1c ;a 1ly anodizingfa@bodyoanlanodizable metalAsuchhl washing and rinsing ofthe pelletaft'er it i sfrer r 1 ov, f the forming-,bath electrolyte. .In pra'oticeit has been n 'ecl'fthe `forming bath, Veach vwashiiigstep being vperformed f dr about two minutesin a separate vat of boilingfdeionized water. inasmuch es the cycle of i anodizing, -impregnati ing, and heatingthepellet usuallyjrepeated five times,

endu/Ctive oxide layrscrve `to`reoxidize1and-heali inboilin-g.wat r .i s abou t one hour. Thujsthe necessityof ythedielectric film in case offpu'ricture ilocal breakdown Carefully washing the pellet `after each yimmersion in the f the'filmn electrolyte cat isesfaigconsiderable increase in the n ranui ,-apdwdered'- acturin-g time, amount oi handling required, and

l method of g1-,cap

anodizable InetalL-is presse toform a `porous body er 25 the Cqst per .u nit. pellet. ,The body` or ,compact thus formed hasy consideri?" Another problem in this process is that slmple immerable surface area but isirathen-frangibleand mec haniea 11yl-n sion" of the Vpellet in the manganous nitrateg solutiondoes weak The` bodyis.- t her e`fore sintered at .-alempeuature not completely impregnatethe pellet pores with thef solur belo he meltingl'ipointof thefi" `articular anodizable' tion.: For thisjreason,.'it"has been commonpractice to' metf thereby ormingapelle'twhic has good rn'echani--3Q use vacuum or pressure impregnationfof vthe manganous ca lstrengthandretfains ahifghdeg'reeifporosity. The vnitrate solution." This practicelrequiresadditional'hansinteredmiletiisimmersed 1n. afbalthontainingl a condnodling` steps,fas v.well as special equipment such as pumps `tivef'electrolyteand janf 'nert'electrdefsuch"as (graphite, and valves. f f i f`lplatinum; andthe like: According-to thegprior` `f`art,"jtlie Accordingly,rit is an object of this Yinvention to provide electrolyte,inayforexample, consist of dilutephosphorie 35` an improved method of fabricating solid electrolytic caor sulfuric acid, .o ranA aqueous'solution'-of .a halogenlpacitors. f Y

substituted acetic acid, or,asoflil'tio'nof- .ammonium bor ratein afglycolsuchas' ethylene glycol. L Fused low-melt-V .proved method of lforming dielectric lrns on anodizable ing salts, such as mixtures of potassium nitrate, sodium electrodes.v f nitrat'e`,andthelike, havealsobeenutilized as theelec- 40 f Another object is to provide a method of simultanetrolyte." The pellet `is made the anode of the bath, and a ouslyforming' a ydielectric-film on an anodizableelectrode current isapiassed'from the pellet through the electrolyte .Q surface and'impregnating the electrode witha compound Vto the inert. electrode, which serves as the bath cathode.' I capable of pyrolytic decomposition into a protective semi- During this step, whichv isknown as'the forming step, cenductive oxide. v f f, a thindielectric iilmconsis'tingof the oxide of thexanodiz 4.5 These and other objects are accomplished by the instant able I ,rietalv is formed-@VGT lthe sui-face of the, pelle't,.andl: invention inthe following manner. A powdered anodiz- .t alsoonfhe finlternalfsurfaceof the pelletifpor'es. There". `ab l el 1net all iis pressed into a porous pellet. The pellet after the pellet is" rer'nfoved fromtheelectrolyte washedv :is vacuum' sintered, then electrolytically treated in -an .-jfive1`times with boiling distilled i deionizedwatendried, :aqueous solution of a compound capable of-pyrolytic ,Anoth r object ofr this invention is.. to providey an im#A "I a `1 1 d dipp ed in asolution of rn-poundfsuch as man`- 5,0 conversioninto'a semiconductive metalloxide.` Thepellet Y ganous nitratewhich is capable of'p'yrolytie conversion is thus anodized, and simultaneously thejpellet -pores it has been necessary to' utilizevery careful and prolonged 1 "ress ary' fto wasll'the pelletvS times 'after eachirrirnersildnin l kfthe totaltimespentiinwashing the wafetWenty-ve times l l to a semiconductive metal oxideflaye'r. The solutionl l lare impregnated with the compound. Subscquently', the

impregnates the pelletpores, sothat on subsequent heatwafer is heated -so as to convert the compound Within the ing a protective layer oiman-ganese oxide is ,formed over pelletpores'into asemiconductive metal oxide. The steps the pellet and within thepellet pores in' close contact to 55 of anodiaing the'pellet and pyrolytically converting the L the `dielectric ilml The` pellet issjanodizedagain, yrinsed :impregnated compound within said pores into the semif iivetimes with boiling distilled Tor deionized water, dried, conductive oxide is usually repeatedtat least once." How-V ag'ain rnpregnated" with the manganous'nitrate solution, eve1',it is no `longer necessary toswash the wafer after andag'ainheated to convert the compound imprcgu'atedr leach "anodization, vsince the same compound used as the in the pellet pores to the protective manganese foxide Goele'ctrolyte in the forming bathV is used to `impregnato laye r. This cycle of anodizing tliefpellct, Washingithe the metal pores and forni azprotective semiconductivela'yer `pellet five Itimes in boiling distilled `Ur deionized ,Wiles v by pyrolytic action. Another advantage is the reduction [drying the pellet, 'irnpregnatngthe pellet with a com in the number `of handling stepsl and manufacturing time "pbllildipble `0f @YTOYUCDVSISOH '0 a SllCOIIfllCI-y per unit, since anodization and impregnation is combined tivernetal5oxidefend heating the waerto'elect'the pylo-` 65 in a single step.' To complete the unit, ia conductive lyticonvljSQnOf 'the ,implgd COmPOl PIO; i coating is deposited uponv the jpellet. Leadvwires are then Vtective met-al oxide layer, is'usually repeated 4about l4 rattached to the pellet' and the conductive coating, and

or 5 times. Thereafterl a conductive coating, is l.,alfiplied the unitis cased by methods known to the art. f

"over the protective metal `oxide layer, leads are v4attached 70 ,Y Theinvention and its advantages willbe described in vitothe bulk of the Vpellet* and to the conductive coating, Y. greater, detail by the following examples and the accom- M1115 .unit is @Sei panying drawing, in which the single lFIGURE is a ow y I the powder Y f l milsl thick:

lf'micronfHg during this step.`

pellet is immersed inaiforming iba: y l Y I electrolyte;` './cco'rding to this iinve'ntion', the electrolyte shetfillustrative-of the varioussteps `in one'embodiment j .of theprocess. f f

Y quantityk oufa powdered anordizlablemetal` is pressed into a porousslugorpellet. Thel aniodizable metal is zirconiumfand: the like. inV Vthis example, thejmetal'is powdered tantalum, and fthe( tantalum particles have a' diameterofjabout 2 to ,4 microns." ,An anode lead 'is providedbyv embedding in the powder a tantalum .ribbon` about Vi'milsv thick, -25 mils wide, and 1/2 inch long. A pressufrelofl abcutjS tons per square inchis'rused'to press finto/'aj` slug or pellet about 1.8 0fmils square Tliejpressed pelletl is lvacuum sintered by heatingfit `for ZOfmIKIutesn.ajvacuum furnace kept atll750,C; The A atmospheric pressure in the furnace `is maintained below The next step is knownfas` the` 'forming step. The

preferably isfn* aqueous solution 'of a compound selected- `from the hydroxides, "nitrates, acetates, yoxalatesA and formates 4of lead, nickel, and manganese. lnthis-example,` the electrolyte is an aqueous solutionV of manganese nitrate,

.selected-1from the group 'consistingv of "aluminumyberylf lium, columbiurn, liafnium, tantalum,titanium,vtungsten,

nitrate'solutiomior example 'a solution containing'raboutcontains `an containingabout58% by we ightgof the solute.The'

electrolyteis"contained in a stainless steel tank,which serves as 'the cathode `of thebath. :The pellet is anodized 'fvoltageA Since injipreg'natio'nv is thus improved, thev number; f

the compound driven into thepellet pores by Vthe applied` .0l weightipercentfor less dissolvedv solute. 1I: Very llittle]- gmanganous nitrate is introduced into the 'pelletpores'dtl'r;.`

inglthis step,'jsince)`the ,electrolytesolution is so dilute. theunit isiov'en fg.

V applied tof theV pellet'V surface .by dipping it nfajsuspenlsionof finely-dividedV gr'apliitel;A TheV graphite-suspension `commercially-available asz'ifiquadagV is suitable for lthisg-:purposef vTo insur a goodruniform coating, thepellet-isjoven drieda'ndlthej l cycle of dipping in Va graphite `suspension andf'drying the.

wafer is-r'epeated. v Aconductivegraphitecoating `is thst y' formed over thepelletsurface. v If. y zx Next 'an electrically conductive silver-loadedgepoxy' `resin''islsprayed over thej graphite coating. A cathode ,lead-'is formed by cementing: a-'nickel ribbonl to the con-1 Y 'ductive `resin layer with'the same epoxy resin.` 'Ihis` bypassing av direct currentffromrthe pellet through the Y electrolyte to the steel tank. @The-voltage applied vranges from about 10 `to l60 volts,depending on the thickness used,'the thicker the resulting film "and the lower/the capacitance of the finished unit. In this example, the

-forming voltage is about 60 volts, andA the pellet is electrolytically treated in the bath for about 11/2 hours. Durof the anodized film` desired.l The/.higher,the voltage Anickel 'ribbon .formsV an electricalY contact through thefY Y vconductive resin layeriand theconductive' graphiteA layer;` i

to the'protective rrianganesey oxide layer whih covers `the Y by methods knowntothe art.Vr An example of r another"einbo Climentofthe invention?Y will now be described. `Thisjenibodifment isgfuseful when.`

ing this step a thin colored dielectric iilm of tantalum' A oxide forms over the pellet surface. The lilrn may be violet, blue, for any of the interference colors depending .upon film thickness, and may vary` in Vthickness from about200 Angstroms to 2000 Angstroms, dependingV on theapplied-voltage and the time it is applied. L Y

The 'pellet is now heatedin airfor about one minutek oxide'. During this step the manganous nitrate Within the pellet pores decomposes, giving olf fumes ofnitric'oxide.

Anon-volatile residue of manganese oxide is left, which it is desirable. to :utilizepformingvoltages greatlyvv in'exf f cess ofV 60 volts.y V'High forming voltages 'a're preferred for the ,production of units which have lower capacity 'ratings `(le, thicker dielectric iilrns)` It hasralsobeen found that Ithe voltage rating 'of iinished capacitor' units v#l5 j'at'500" C. Vto eifect the pyrolytic conversionv of the l manganous nitrate within the pellet pores to manganese A quantity of a powdered'anodizablermetal is formed, l 1

closely covers and adheres to the` dielectric 'tantalum oxide lilm. f f i The pellet is now readyfor a repetitionl of the cycle K rvofanodization followed by pyrolytic conversionr of the .vimpregnated :compound to the protective metal oxide.

Anodization is again accomplished in an electrolyte conis directly related to the forming voltage during the fabrication lof the units, hence capacitors intended to exhibit a high voltage rating are anodized at high voltages.

Example `Il Y `into a porous pellet about 180 mils square and 10 mills thick by fappglying a 'pressurefjof about 450 Ypounds toV H w .the powder. `Inv this example, the anodizablefmetlalisb colfumbium. The pellet isryaeuum'snteredat 1500? G for 15 minutes. An Ianode lead is formed by spot-'Weld-VA V. 'ing to the pellet a columbi-um ribbon about 3 milsthick',

sisting of aqueous manganous nitrate solution. The' bath `.containing 58% by weight manganous nitrate-solution, which was used inthe tir-str anodization, may be lused in the subsequent anodization steps.Y i However, the voltage applied during all anodizationV steps after Vvthe first step is preferably lowerlthan the voltage appliedfduringthe irst forming step, in order to avoid increasing the thickl, ness of the rdielectric film. In this example, all the subi sequent anodization steps are accomplished by applying a voltage of about 45 volts for about 45 vminutes to the pellet in the forming bath.

An important feature of this invention is that the prolonged` and careful washing of the pellet required in the prior Vart is not necessary, since a solution ofthe same compound is used for the various anodization steps and impregnationsteps. Another feature is thatV the impreg- `nation of the electrolyte compound solution within the pellet poresv is more thorough than that obtained by merely immersing the pellet in a solution, since in effect f 25 mils wide, Vand 1A; inch long..v The resintered at 1500 C. for 15 minutes. Y

The pellet is now placed in' a forming bath, which in this example contains an aqueous solution of nickel nitrate as theelectrolyte. i, rSince it is desired to perform thefiirst anodization fata high voltage, a dilute solution i 1 of the electrolyte is employed for the first forming step, v

as concentrated electrolyte solutionstend to break down pellet is i then t atl high voltages. In this` example, the aqueous electro` .lyte utilized in the irstforming step` contains about .01 f

Weight'percent nickel nitrate. Asinthe previous ex-l ample, the electrolyte is contained Yina' stainless steek.` tank which serves'fas theV cathode of thejbath.` The pellet *is anodized by passinga direct current from `the pellet,`

.1 -thrOugIELfLheelectrolyte tothe; steel tank. In this example, the first anodizationis performedjat 180 volts for minutes. A dielectric lm of. columbium oxidel is thereby formed over the pellet.` The nnit is now dried by heating it in air for l5 minutes at 110 C.

Next, the pellet is immersed in af saturated 'aqueous solution of nickel nitrate, :andreformed by the application `of 50 lvolts for 30 minutes. During this step the pellet pores become impregnated with nickel nitrate. Theipellet is then heated about one minute at'450o C.

toeliect the pyrolyticv conversion of the impregnated nickel nitrate to a protective layer of nickel oxide which tion `is performed for 30` minuts at 50 volts in a dilute and the penal is Oven dried minutes at 110 C. i

A vconductive coatingY is now applied to the pellet surface. The coating may for example consistiof graphite, applied in the manner described above inEx- Y amplel. Next, a portion of the wafer adjacent to the anode lead is masked, and the remainder of the pellet sprayed V with 60 tin-40 lead solder. A cathode lead is formed by soldering a gold plated nickel ribbon to the solder coated area of the pellet. VThe gold plated ribbon -orms 1an electrical contact through the solder and the conductive graphite to the layer of nickel oxide which covers the dielectric columbium oxide tilm. The unit is then cased by methods known to the art.

It will be understood that the above examples were by wayV of illustration only, and not as limitations.

Many rntxlicationsV may be made in the process without departing from the spirit and scope of the instant invention. 'For example, any of the other anodizable metals may be utilized, such as titanium 'and the like. Other `serniconduct-ive metal oxides such as'lead oxide may be utilized for the protective layer over the dielectric film.

2; The method of fabricating a solid electrolytic capacitor comprising the following steps: pressing -a powdered anodizable metal into a porous pellet, said metal being selected from the group consisting of aluminum, k beryllium, columbium, hafnium, tantalurn, tungsten, and

zirconium; vacuum sintering rsaid pellet; elcctrolytically treating said pellet in a concentrated laqueous s-olutionof k :a compound capable of pynolytic conversion into a semi- The electrolyte may be any compound of lead, nickel, l l

or manganese .whichl is readily vpyrolyzed and leaves a residue consisting of the oxide oflead, nickel, or man'- ganese.

What is claimed: f

1. 'Ihe method of forming a solid electrfoyltic capacitor `so las to convert said compound, which has been thus electrolytically introduced, in said pellet pores into a conductive metal oxide soasv to simultaneously anodize said pellet and impregnate the pellet pores with said compound; heating said wafer so as to convert said compound, which Ihas been thus elec-trolytically introduced, in said pellet pores into a semiconductive metal oxide;

repeating at least once the steps of anodizing said pellet and pyrolytically converting the impregnated compound within said pores into a semiconductive metal oxide; and depositing a conductive coating upon said pellet.

Y3. The method of iorming la solid electrolytic capacitor'cornprising the `following steps; pressing a powdered lanodizable metal into a porous pellet; vacuum sintering said pellet; electrolytically treating said pellet in a concentrated'aqueous solution of a compound rcapable of pyrolytic conversion into la serniconducti've metal oxide selected from the group consisting lof lead oxide, nic-kel oxido, land manganese oxideso as to simultaneously anodize said pellet and impregnate thepellet pores with said compound; heating said wafer so as to convert said compound, which has been electrolytically introduced, in said pellet pores into a semiconductive meta-l oxide; repeating at least fonce the steps of anodizing said pellet and pyrolytically converting the impregnated compound within said pores into a semiconductive metal oxide; and depositing a conductive coating uponsaid pellet.

,4;The method of fabricating a .solid-electrolytic capacitlor comprising the following steps: pressing a powdered yanodizable metal into a porous pellet; vacuum sintering said pellet; electrolytically treating said pellet in la Vconcentrated aqueous solution of a compound selected v yfrom the group consisting ofthe hydroxides, nitrates, acetates, oxalates, and yormates of lead, nickel, and manganese so `as to simultaneously anodize said pelletand impregnate the pellet pores with said compound; heating said wafer so as to convert said compound, which has stmiconductve metal oxide; repeating at least once the steps of anodizing said pellet and pyrolyt-ically converting the impregnated compound vvithin said pores into been electrolytically introduced, in said pellet pores into a semiconductive metal roxide; repeating at least once the steps of anodizing said pellet and pyrolytically converting the impregnated compound with-in said pores into a semiconductive metal oxide; :and depositing a conductive coating upon said pellet.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF FORMING A SOLID ELECTROLYTIC CAPACITOR COMPRISING THE FOLLOWING STEPS: PRESSING A POWDERED ANODIZABLE METAL INTO A POROUS PELLET; VACUUM SINTERING SAID PELLET; ELECTROLYTICALLY TREATING SAID PELLET IN A CONCENTRATED AQUEOUS SOLUTION OF A COMPOUND CAPABLE OF PYROLYTIC CONVERSION INTO A SEMICONDUCTIVE METAL OXIDES SO AS TO SIMULTANEOUSLY ANODIZE SAID PELLET AND IMPREGNATE THE PELLET PORES WITH SAID COMPOUND; HEATING SAID WAFER SO AS TO CONVERT SAID COMPOUND, WHICH HAS BEEN THUS ELECTROLYTICALLY INTRODUCED, IN SAID PELLET PORES INTO A SEMICONDUCTIVE METAL OXIDE; REPEATING AT LEAST ONCE THE 